Chymosin has been separated and purified using various techniques. For example, calf rennet or rennet extracts have been purified using blue dye affinity ligands, as in U.S. Pat. No. 4,666,843 to Subramanian or using a cellulose resin column, as in U.S. Pat. No. 4,745,063 to Birschbach. The same methods have been used to recover and purify microbially produced chymosin, as in U.S. Pat. No. 4,743,551 to Subramanian and U.S. Pat. No. 4,721,673 to Uren et al., respectively. The disclosures of these patents are incorporated herein by reference.
However, in industrial or commercial scale production of chymosin by microbial activity these methods of recovery and purification of chymosin are inadequate. For commercial scale industrial production, more efficient, more economical methods of recovering and purifying chymosin are needed. It is also essential that such processes be adaptable to economic scale-up for commercial production.
Of particular interest in the industrial microbial production of chymosin is the production of chymosin by fermentation of filamentous fungi which have been genetically modified to express and secrete chymosin, as disclosed in U.S. patent application Ser. No. 163,219 of Lawlis et al. filed Feb. 26, 1988, abandoned in favour of U.S. patent application Ser. No. 07/413,010 filed Sep. 25, 1989 incorporated herein by reference.
It is an object of this invention to provide efficient processes for the separation and purification of chymosin from aqueous mixtures of enzymes, particularly aqueous mixtures produced by fermentation or other microbial activity and particularly for commercial scale production of chymosin.